It occurs to me that, if you're in any doubt about the legality of what you are planning, you could always ask the Univ. of Illinois for their permission to convert their 1956 edition into an ebook. If it's out of print, and if they have no plans to publish it as an ebook themselves, they might just give you the OK. Just a thought.

In any case, good luck with this project.

IANAL, but I think you'd need to contact George Willard White (or his heirs), since he's the copyright claimant on the copyright renewal on the new material. The original material is public domain, so if you knew for sure that your conversion to ebook only contained the contents of the original book, there's no need to contact the reprint's publisher. Obviously, this is easier to do with the facsimile reprint, but if you have access to the original work, you'd know what's new and what's original.